Ad hoc networks are communication networks without a fixed infrastructure. A number of wireless stations are equipped with radio transceiver means and appropriate protocols for forming the ad hoc network.
These stations making up the ad hoc network can be in the form of fixed or portable computers, pocket computers, mobile telephones, vehicles, electrodomestic appliances, etc. The transceiver means can also be associated with simple objects such as sensors or actuators. An ad hoc network of sensors thus makes it possible to collect information for example with a view to monitoring or checking installations.
The success of ad hoc networks depends a great deal on the lifetime of the stations constituting the nodes of the network. Energy saving is a crucial factor when designing sensor networks with a long lifetime, in particular because the nodes are generally powered by batteries which are generally expensive and difficult, or indeed impossible, to replace or recharge.
Routing in a telecommunications network comprises the process of searching for a route between a source node, transmitting data, and a destination node, receiving the data. The route is the succession of nodes of the network that the data will follow between the source node and the destination node.
In wireline networks, it is conventional to select the best route as that which will most rapidly provide the response. Routing is then performed in accordance with a delay minimization algorithm.
In the context of wireless communications, such a delay minimization algorithm can also be used. Its advantage is the low complexity of processing of the management messages exchanged between the nodes of the network to establish the best route. This type of algorithm also reduces the overhead of the routing protocol.
To illustrate the operation of a delay minimization routing algorithm, reference is made to FIG. 1, which schematically shows an ad hoc network composed of five stations A-E, of which station A (for example a micro-computer) constitutes the destination node of the data, often called the “sink”. It is considered here that node E is the source of the data.
To initiate the collection of the data, the sink A broadcasts a request message to search for sources. Each of the intermediate nodes B and C receives this request, processes it, then rebroadcasts it. Node D receives the request twice, once from B, and once from C. Node D processes only the first request that it receives, and ignores the second. Node D rebroadcasts the request received first. This rebroadcast is received by nodes B and C, and each of them ignores it, given that it is an already received request. Node E receives the request broadcast by B. As it is able to provide the expected data, it responds to the request by returning these data. The response message sent back by E makes it possible to identify the request. The intermediate node B has remembered that this request originated from node A, so that it forwards the response to this node A.
It is possible to verify that in such a delay minimization routing algorithm, the intermediate nodes broadcast only a single message and process only a single message.
But a drawback of the known delay minimization routing algorithms is that they do not make it possible to optimize the duration of proper operation of an ad hoc network. Specifically, the routing is performed without taking account of the energy level available at the nodes.
For example, in the case of FIG. 1, node B serves to forward not only the traffic coming from node E, but also part of the traffic whose source is node D (or even the entirety if the route ABD is systematically faster than the route ACD). Consequently, the electrical consumption of node B will be much greater than that of node C. As soon as the battery of node B fails, the ad hoc network is no longer operational. It is seen that its lifetime would have been greatly increased if the intermediate node C had been used preferably to trunk the traffic originating from D.
To alleviate this type of drawback, other families of routing algorithms have been designed for ad hoc networks. These algorithms choose the routes as a function of a metric that can take account of the residual energy of the intermediate nodes. Typically, such an algorithm chooses the routes which globally consume the least energy when all the nodes have a high energy reserve, and avoid the routes containing nodes whose residual energy is low even to the detriment of the global energy. See for example C-K. Toh, et al., “Performance Evaluation of Battery-Life-Aware Routing Schemes for Wireless Ad Hoc Networks”, Proceedings of the IEEE ICC, Helsinki, June 2001, pages 2824-2829.
To illustrate these algorithms aimed at maximizing the lifetime of the network, reference is again made to FIG. 1, now assuming that node D is able to provide the response expected by the sink A. On receipt of the request sent by the sink A, each of the intermediate nodes B and C processes it by adding thereto an attribute determined as a function of its respective residual energy. This attribute allows each node which receives a request to ascertain the quantity of residual energy on the path from which it originates. The quantity of residual energy on a path corresponds here to the residual energy of the node having the lowest energy level along this path. The source node D must then process each of the two requests received from B and from C so as to decide which route to take as a function of the residual energy attribute included in each request received.
The drawback of this type of algorithm is that each intermediate node must process all the requests that it receives to update the residual energy field in the request that it will rebroadcast. This results in more complex processing in the intermediate nodes, for the reception and processing of all these requests. This is unfavorable to electrical consumption.
Moreover, to receive all the requests whose instants of arrival it does not know a priori, a node must wait a certain guard time which is difficult to adjust (too short a time causes premature decisions to be taken, while too long a time unnecessarily increases the latency of the processing). Moreover, the use of an additional attribute in the requests increases the size of the management messages (overhead), thereby also increasing energy consumption.
An object of the present invention is to simplify the routing techniques using routing metrics to optimize the performance of a telecommunications network, in particular in terms of lifetime in the case of ad hoc networks.